Upper level and phase controlling group velocity in V-type system

With the external field coupling the two upper levels, we investigate the light pulse propagation properties with weak probe field in a V-type system. Due to the external upper level (UL) coupling field, the dispersion of the system has been influenced by the relative phase. It is shown that the UL field and the relative phase can be regarded as switches to manipulate light propagation between subluminal and superluminal. (c) 2007 Elsevier B.V. All rights reserved.

Optical solitons in a four-level inverted-Y system

With one weak probe field and two strong pumping fields, the possibility of producing superluminal optical solitons is discussed in a lifetime-broadened inverted-Y atomic medium with proper parameters. As the group velocity of the solitons is larger than c, its occurrence can be controlled by modulating the intensities and the detunings of lasers.

The dispersive properties of an excited-doublet four-level atomic system

We have investigated the dispersive properties of excited-doublet four-level atoms interacting with a weak probe field and an intense coupling laser field. We have derived an analytical expression of the dispersion relation for a general excited-doublet four-level atomic system subject to a one-photon detuning. The numerical results demonstrate that for a typical rubidium D1 line configuration, due to the unequal dipole moments for the transitions of each ground state to double excited states, generally there exists no exact dark state in the system. Close to the two-photon resonance, the probe light can be absorbed orgained and propagate in the so-called superluminal form. This system may be used as an optical switch.

Optimization of nonvolatile holographic recording by application of an external electric field

The dependences of the recording properties of LiNbO3:Fe:Mn crystals on an external electric field (applied in the recording or fixing phase of the nonvolatile holographic recording process) are numerically investigated and the optimal conditions for applying an external electric field in this two-step process of nonvolatile holographic recording are discussed in detail. Significant improvement of the photorefractive performance has been found and experimental verifications using a small external electric field are described. Moreover, direct measures relating to the dominant photovoltaic mechanism in the doubly doped LiNbO3 crystals and the unconventional grating-enhanced fixing are revealed by applying an external electric field in the recording and the fixing phases, respectively.

Phase-locking of two large-core fibre lasers with 60W of coherent output power

A phase-locking fibre laser array with up to 60 W of coherent output power based on two large-core fibre is reported. The slope efficiency of the in-phase mode is 37%. For two cases of spacings between the cores, steady high-contrast interference stripes are observed. When the whole system operates under a high pump power level, no thermal effects for the spatial filter have been observed, which means that we can increase the coherent output power further by increasing the individual fibre laser power.

Is there a genetic relationship between mRNA and the encoded protein at three-dimensional level?

A comparative study on the structures of some mRNAs and their encoded proteins shows an intriguing correlation between the two foldings. Non-random distribution of codons in the secondary structures of mRNAs is also shown, which appears to be in accordance with the conformational properties of amino acids in protein structures to some extent. These results seem to suggest that there may be a kind of genetic relationship between mRNA and protein at three-dimensional level.

Distribution of 25 semi-volatile organic compounds of two urban lakes in Wuhan, China

In this study, the levels of 25 semi-volatile organic compounds (SVOCs) were measured in samples of water, suspended particulate matter (SPM) and sediment from two urban lakes in Wuhan, China. The total concentrations of 25 SVOCs varied from 529.4 to 2168.9 ng/L, 120.7 to 22543.7 ng/g dry weight and 1577.3 to 61579.6 ng/g dry wt. in water, SPM and sediment, respectively. The concentration of SVOCs in SPM was 9-10 times higher than that in water, and the concentration of SVOCs in sediment 1.5-2 times higher than that in SPM. The level of total SVOC25 in the samples from Moshuihu Lake was higher than that in Yuehu Lake. Among the 25 SVOCs, phthalate compounds were on the highest level in all observed samples ranging between 441.9-1831.2 ng/L, 116.3-17566.8 ng/g, dry wt. and 6432.8-48177.6 ng/g dry wt. in water, SPM and sediment, respectively. Bis(2-ethylhexyl)phthalate, the predominant component of the analyzed pollutants, was in the range from 246.7 to 537.5 ng/l, 51.2 to 15540.0 ng/g dry wt. and 468.2 to 45010.3 ng/g dry wt. in water, SPM and sediment, respectively. The content of PAHs, dinitrotoluene and isophoton in sediment was higher than that in water and SPM at most of the locations. The possible sources of the pollutants and their inter-relation with human activities were discussed.

Utility of ITS1-5.8S-ITS2 sequences for species discrimination and phylogenetic inference of two closely related bucephalid digeneans (Digenea : Bucephalidae): Dollfustrema vaneyi and Dollfustrema hefeiensis

The complete internal transcribed spacer 1 (ITS1), 5.8S ribosomal DNA, and ITS2 region of the ribosomal DNA from 60 specimens belonging to two closely related bucephalid digeneans (Dollfustrema vaneyi and Dollfustrema hefeiensis) from different localities, hosts, and microhabitat sites were cloned to examine the level of sequence variation and the taxonomic levels to show utility in species identification and phylogeny estimation. Our data show that these molecular markers can help to discriminate the two species, which are morphologically very close and difficult to separate by classical methods. We found 21 haplotypes defined by 44 polymorphic positions in 38 individuals of D. vaneyi, and 16 haplotypes defined by 43 polymorphic positions in 22 individuals of D. hefeiensis. There is no shared haplotypes between the two species. Haplotype rather than nucleotide diversity is similar between the two species. Phylogenetic analyses reveal two robustly supported clades, one corresponding to D. vaneyi and the other corresponding to D. hefeiensis. However, the population structures between the two species seem to be incongruent and show no geographic and host-specific structure among them, further indicating that the two species may have had a more complex evolutionary history than expected.

Molecular cloning of growth hormone receptor (GHR) from common carp (Cyprinus carpio L.) and identification of its two forms of mRNA transcripts

The cDNA of growth hormone receptor (GHR) was cloned from the liver of 2-year common carp (Cyprinus carpio L.) by reverse transcription-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA end (RACE). Its open reading frame (ORF) of 1806 nucleotides is translated into a putative peptide of 602 amino acids, including an extracellular ligand-binding domain of 244 amino acids (aa), a single transmembrane domain of 24 aa and an intracellular signal-transduction domain of 334 aa. Sequence analysis indicated that common carp GHR is highly homologous to goldfish (Carassius auratus) GHR at both gene and protein levels. Using a pair of gene-specific primers, a GHR fragment was amplified from the cDNA of 2-year common carp, a 224 bp product was identified in liver and a 321 bp product in other tissues. The sequencing of the products and the partial genomic DNA indicated that the difference in product size was the result of a 97 bp intron that alternatively spliced. In addition, the 321 bp fragment could be amplified from all the tissues of 4-month common carp including liver, demonstrating the occurrence of the alternative splicing of this intron during the development of common carp. Moreover, a semi-quantitative RT-PCR was performed to analyze the expression level of GHR in tissues of 2-year common carp and 4-month common carp. The result revealed that in the tissues of gill, thymus and brain, the expression level of GHR in 2-year common carp was significantly tower than that of 4-month common carp.

Tissue distributions and seasonal dynamics of the hepatotoxic microcystins-LR and -RR in two freshwater shrimps, Palaemon modestus and Macrobrachium nipponensis, from a large shallow, eutrophic lake of the subtropical China

So far no information is available on microcystin (MC) contents in shrimps, prawns or crayfish from natural freshwaters. Tissue distributions and seasonal dynamics of the hepatotoxic MC-LR and -RR in two freshwater shrimps, Palaemon modestus and Macrobrachium nipponensis were studied monthly (during June-November, 2003) in a Chinese lake containing toxic cyanobacterial blooms. The shrimps P. modestus and M. nipponensis accumulated high MCs not only in the hepatopancreas (mean 4.29 and 0.53 mu g g(-1) DW, respectively) but also in the gonad (mean 1.17 and 0.48 mu g g-1 DW, respectively), and the crayfish Procambarus clarkii accumulated as much as 0.93 mu g g(-1) DW in the gonad. This indicates that gonads of these invertebrates are the second important target organ of MCs. P. modestus apparently accumulated more MCs in their organs than M. nipponensis, which might be a reflection of their difference in trophic niche. Eggs of the shrimps accumulated 8.4% (M. nipponensis, 0.27 mu g g(-1) DW) and 29.0% (P. modestus, 2.34 mu g g(-1) DW) of total toxin burden, indicating that MCs had been transferred into offspring from their adults. Among the shrimp muscle samples analyzed, 31% were above the provisional WHO TDI level, suggesting the risk of consuming shrimps in Lake Chaohu. (c) 2005 Elsevier Ltd. All rights reserved.

Characterization of two membrane-associated protease genes obtained from screening out-membrane protein genes of Flavobacterium columnare G(4)

In order to identify genes encoding the outer membrane proteins (OMPs) of the myxobacter Flavobacterium columnare G(4), the expression library of the bacterium was screened by using rabbit antisera developed against its OMPs. Positive colonies of Escherichia coli M15 containing fragments encoding the bacterial OMPs were selected for cloning the relevant genes by genomic walking methods. Two genes encoding a membrane-associated zinc metalloprotease and prolyl oligopeptidase are reported in this paper. The membrane-associated zinc metalloprotease gene (map) is 1800 bp in length, coding for 449 amino acids (aa). Despite the presence of a conserved motif HEXXH for all metalloproteases, the special HEXXH similar to 32 aa similar to E motif of the F. columnare G(4) Map and its low level of identity with other reported zinc-containing metalloproteases may imply that the membrane-associated zinc metalloprotease of F. columnare G(4) represents a new family of zincins. The gene encoding prolyl oligopeptidase (Pop), a serine proteinase, is 2352 bp in length, coding for 649 aa. Sequence homology analysis revealed that the Pop is also novel as it has <50% identity with other reported prolyl oligopeptidase family proteins. The present study represents the first to employ anti-fish bacterial OMP sera to screen genes of membrane-associated proteases of fish pathogenic bacteria, and to provide necessary information for the examination of the role of the two genes in the infection and pathogenesis of F. columnare.

Identification and expression analysis of two IFN-inducible genes in crucian carp (Carassius auratus L.)

Interferon (IFN) exerts its antiviral effects mainly through activation of a subset of IFN-stimulated genes (ISG), but relatively few of fish ISGs have been isolated and characterized so far. Here, we report two fish ISGs, termed CaIF158 and CaIF156, cloned from a subtractive cDNA library constructed with mRNAs obtained from crucian carp (Carassius auratus L.) blastulae embryonic (CAB) cells infected by UV-inactivated GCHV and mock-infected cells. Database search revealed that both ISGs had a high-level homology with all members of a well conserved gene family with multiple tetratricopeptide repeat (TPR) motifs, including human IF160, IF158, IF156, IFI54 and their homologues in some other mammalian species. The transcripts of CaIF158 and CaIF156 were undetectable in CAB cells but could be induced by active GCHV, UV-inactivated GCHV or CAB IFN. Analysis of expression difference between them and IFN signal factors, CaSTAT1 and CaIRF7, indicated that their transcriptions were mediated possibly through JAK-STAT signal pathway, which was further supported by the induction analysis in UV-inactivated GCHV infected, IFN-treated and untreated cells in the presence or absence of cycloheximide (CHX), a potent inhibitor of protein synthesis. In addition, a pufferfish (Fugu rubrides) DNA sequence representing putative FrIFI56 was also revealed when CalF158 and CalF156 were used to search the pufferfish genome database. Phylogenetic analysis showed that these fish ISGs form a unique clad independent of mammalian homologues, reflecting a distant evolutionary relationship from mammals. These studies identified the first teleost IFI56 and IFI58 orthologues. (C) 2003 Elsevier B.V All rights reserved.

Growth and feed utilization in two strains of gibel carp, Carassius auratus gibelio: paternal effects in a gynogenetic fish

Gibel carp (Carassius auratus gibelio Bloch) is a natural gynogenetic fish which requires sperm of the same or related species to activate egg development. The eggs of one gibel carp were divided into two batches. One batch was 'fertilized' with sperm from gibel carp (strain DD), and the other 'fertilized' with sperm from red common carp (Cyprinus carpio red variety) (strain DR). The juveniles were transferred to the laboratory 36 days post-hatch. Triplicate groups of each strain were fed a formulated diet at either 3% or satiation ration for 8 weeks. At both the restricted and satiation rations, specific growth rate was significantly higher in strain DR than in strain DD. At the 3% ration, there was no significant difference in feeding rate or feed conversion efficiency between the two strains. At the satiation ration, strain DR had a significantly lower feeding rate but higher feed conversion efficiency than strain DD. At the satiation ration, strain DR had a significantly lower intake protein, but higher recovered protein than strain DD. There was no significant difference in faecal protein loss between the two strains. At the 3% ration, strain had no significant effects on intake protein, faecal protein or recovered protein. Neither faecal energy loss nor recovered energy was affected by strain or ration. At both the 3% and satiation ration, final body contents of dry matter and lipid were significantly lower in strain DR than strain DD, while there was no significant difference in protein and energy content between the two strains at either ration level. The results suggested that gibel carp 'fertilized' with sperm of common carp grew faster than those 'fertilized' with sperm of gibel carp through increased feed conversion efficiency and protein retention.

RAPD and AFLP techniques for the analysis of genetic relationships in two genera of Decapoda

RAPD was used fur analysing three (sub-)species of mitten crabs (Eriocheir sinensis, E. japonicus, and E. japonicus hepuensis) and three populations of E. sinensis. The results show that their relationships on DNA level are similar to the classical taxonomic hypotheses (Dai, 1991). No diagnostic RAPD marker could be found, but there were statistically significant genetic differences among these taxa (P < 0.001) or populations (P < 0.001). That is, the intraspecific similarities were larger than the interspecific similarities; the intrasubspecific similarities were larger than the intraspecific similarities; and the intrapopulational similarities were larger than the interpopulational similarities. In AFLP analysis, no significant genetic difference has been found between E. sinensis and E. japonicus, but AFLP markers among four species of Macrobrachium (M. rosenbergii. M. nipponense, M. hainanense, and M. asperulum) were found. The DNA similarities among these four species of Macrobrachium are in accordance with morphological similarities.

Exact result for the Green's function of a two-dimensional interacting electron gas with spin-orbit interaction in a perpendicular magnetic field

An exact property is established for the Green's function of a uniform two-dimensional interacting electron gas in a perpendicular magnetic field with spin-orbit interaction. It is shown that the spin-diagonal Green's function is exactly diagonal in the Landau level index even in the presence of electron-electron interactions. For the Green's function with different spin indexes, only that with adjacent Landau level indexes is non-zero. This exact result should be helpful in calculating the Green's function approximately.